Kisame has way more chakra reserves then Zabuza plus the samehada can eat chakra from zabuza even with zabuza using his sword and kisame is strong enough to go toe toe with any tailed beast since his chakra reserves are closey similar to a jinjuriki for example i cannot see zabuza wining against Killer bee but kisame yes ( which almost happened. not to mention kisame fused shark thing and his water bubble thing how zabuza is escaping that furthermore kisame took down that entire hidden mist division team and on e shotted fugal who had the samehada at the time.
